Topping governor and reversing solenoid for variable pitch propellers



M. E. LoNGFELLow ETAL 2,664,960

Jan. 5, 1954 TOPPING GOVERNOR AND REVERSING SOLENOID FOR VARIABLE PITCHPROPELLERS 3 Sheets-Sheet 1 Filed July 29, 1950 INV NToRs Melvin Langfe/nw. BYNEsanRRiclzmand AG E N T Jan 5, 1954 M. E. LoNGFELLow ETAL2,664,960

TOPPING GOVERNOR AND REVERSING SOLENOID n FOR VARIABLE PITCH PROPELLERSl Flled July 29, 1950 3 Sheets-Sheet 2 ToPRoP'LLz/v CoNTroL .frana/varyP/.s v-o/v .55m/a CONTROLLI? /NPuT .Marr/Y INVENToRs AGENT Jan- 5, 1954M, E. LoNGFELLow ETAL 2,664,960

TOPPING GOVERNOR AND REVERSING SOLENOID FOR VARIABLE FITCH PROPELLERS 3Sheets-Sheet- 3 Filed July 29, 1950 M. .bm

lllllll AGENT Patented Jan. 5, 1954 TOPPING GOVERNOR AND REVERSINGSOLENOID FOR VARIABLE PITCH PRO- PELLERS Melvin E. Longfellow,Manchester, and Nelson R. Richmond, Thompsonville, Conn., assgnorstoUnited Aircraft, Corporation, East Hartford, Conn., a corporation ofDelaware Application July 29, 195o, serial No. 176,578

s claims. (o1. 17o-160.2)

This invention relates to improvements in aircraft propellers and morespeciiically to variable pitch propellers having improved control meanstherefor.

It is an object of this invention to provide an improved pitch controland operating mechanism for variable pitch propellers.

A further object of this invention is to provide a variable pitchpropeller control system comprising normal governing means and includingan overspeed governing system which can be by-passed during operation ofthe propeller pitch reversing control mechanism.

Another object of this invention is to provide a topping or overspeedgoverning mechanism cooperating with a pitch reversing mechanism in apitch control system of the type described herein. A f

These and other objects will become readily apparent from the followingdetail description of the accompanying drawings in which:

7Fig. 1 is a schematic illustration of a propeller and associated geartrain for transmitting controlling movements from the control system tothe hub carried pitch changing mechanism.

Fig. 2 is a schematic illustration of the propeller control system ofthisinvention with the elements arranged as a continuity of Fig. 1.

Fig. 3 is an electrical diagram of the propeller control system.

Referring to Fig. l, a propeller is illustrated as being operativelyconnected by a driving element or gear it which may form a part of aturbine or reciprocating piston power plant and which also serves todrive a tachometer generator l2 which in turn transmits electricalenergy to ran electronic governor schematically shown at`l4. rEheelectronic governor may be of the type shown in Patent No. 2,517,703issued August 8, 1950. The electronic governor in turn both receives andtransmits electrical signals to the propeller control system as willbecome apparent hereinafter. The electronic governor of theabove-referred to patent would have its components connected in thepresent system as follows. Thus for kexample the generator in the patentis the lequivalent of the tachometer generator I2 whilerthe proportionalsolenoid respondsKL similar to that illustrated in Fig. 2 hereof. frlherieedback potentiometer shown in the drawings may be connected inthe with each of the blades having fluid operated vane motors 24 mountedwithin the shanks thereof. TheA vane motors 24 respond to high pressureiiuid to vary the pitch of the blades in a low pitch or high pitchdirection, as indicated by the arrows, it being noted that the lettersLP and HP are used in the drawings to indicate said same manner asvthepotentiometer H1 of Fig. 5

of the above-referred to patent. e

The propeller illustrated herein comprises a hub 2G which may haveaplurality of radially eX- tending variable pitch blades 22 mountedtherein pitch directions respectively.

The propeller hub 20 carries the entire pitch actuating mechanisminternally thereof including an integral hydraulic reservoir, the actualconstruction of which is more clearly illustrated and described incopending application Serial No. 154,857, led April 8, 1950, by ArthurN. Allen, Jr.

A pressurized sump 3U is provided for supplying uid to a high pressuremain pump 32 and a stand-by pump 34 by means of hydraulicr lines 36 and38, respectively. The sump 38 is pressurized to some nominal value bymeans of a scavenge pump 40 which receives uid from an oil chamber (notillustrated) under atmospheric pressure. The sump `3l] is maintained atthis predetermined normal pressure by means of a sump relief valve 42which dumps relieved iuid back into the above-mentioned chamber which isunder atmospheric pressure. High pressure uid from the pumps 32 and 34is directed to a distributor valve generally indicated at 46 whichcontrollably directs this high pressure fluid via the lines 48 or 5D toeither side of the vane motors 24 for varying the pitch of the blades22. Since the capacity of the main pump 32 is suflicient for normalpitch changing movements, the, output of the stand-by pump 34 isdirected from the line 52 around the land 54 of the distributor valve 46and then to the port 56 or the valve to a central drain passage 58therein.

When the demand for pitch changing movements is high, as reflected bylarge movements of the distributor valve, the land 54 will close 01T theincoming iluid from the passage 52 so that the pressure in the passage42 will immediately build up suiliciently to open the check valve tesothat an additional volume of iiuid will be available forpitch changingmovement to supplement the flow of high` lpressure iiuid coming from themain pump 32 via the line 82.

The central portion ofthe distributor valve 46 is actuated inreciprocating motion by means shaft 18 the valvec'entral portion/will bereposi-k tioned when the blade interconnecting gear 80 is rotated by thegear segments 82 (carried by the blade 22) during pitch changingmovements of the blades.

A positr've'raitchet type pitchloc'k'l is provided. for automaticallylocking the blades against pitch changing movements in a low pitchdirection in the event of failure oir-.hydraulic pressure in the system.A spring SZbiases @pitch lock piston 04 toward a lock position whilefluid under pressure flowing via the line 95 forces the piston 94 towardan unlocked position. "Ihe'rluidunder pressure in the line 96 is fed viaja'passa'g'e which surrounds the follow-up shaft 'T8 'an'd normallycommunicates with the central drain chamber of the distributor valve Viaa port 588, :the la-n'dfadjacent the port 98 normally permittingfluid-communication to the pitch `lock piston. "I'liedra'in pressurewithin the central chamber 58 of the distributor valve is 'maintainedlat 'some' vpredeterminedfvalue `slightly `above Vthe pressure of vtheJ30by means of ja pitch 'lockreliefvalve which is illustrated in the endofthe distributor valve46.

'The pitch lock system shown herein 4is 'more 'fully described and'claimed in ico-pending vapplication Serial No. 129,082, led November23, 1949, by'Erle-Martin-and Thomas B. Rhines now U. S. Patent SerialNo. 2,653,671, issued VSeptember 29, V1953.

The propeller parts described thus far are `contained withinfor form'apart of, the rotatable hub portion of the propeller assemblyandthe'mechanism hereinafter described is carried in stationary housing'held fixed relative to theassociated power plant. To this end, then, apair of vintegral'gears -||0 and |2'are normally fixed'so that duringIpropeller rotation the gears I I4 -and `H6 which engage the gear ||0will reivolve thereabout and in so doingfwill provide a rotational drive'for the main pump 32 and the Stand-*by pump 84. The scavengepump40contained I-wlthin the propeller 'hub will 4likewise lbe 'drivln'glyrotated through'its gear `||8"which also l'engz'iges-thenormallystationary gear ||0. A'seco'nd'pair of integral gears |20and |22 are,during -an'on-speed'propell'er condition, normally rotated atthe vsamespeed asthepropellerby'meansof an 'epleyelic gear train generally'indicated vat A'|26 `which -train is driven -by a gear '|28 connected'torro'tation ywith vthe propeller 'and `its drive "shaft The gear |20'(which normally 'rotates'at `prop'elli'er speed) engagesadistributorivalve driving gear v|30 Awhich Ais xed to the distributorvalvefdriving nut 10. `It'is th'enapparent'th'atLduringan-onspeedcondition with the gears' |20 and |22 rotating ataspeed'identical topropeller lrotation, thedistributor valve'drive gear|30 Will 'remain'stationary -so as `not to ldisturb-the setting of lthedistributor lvalve 46. l

The epicyclic gear train 26 comprises a shaft F40 on Which'all o'f'thegears thereon are mounted freely. The gears |42 and |44 are connectedlftogether for simultaneous rotationy'as are `also forms the `planetarycage. A control gear |00 Aisflxed to a shaft |62-andis driven via thebevel `gears .|64 by "the'servo control output shaftl68. During 'anonspeed conditionithen,"witlrthe servo Ycontrol output shaft |68stationary, 'the -`control gear |60 will also remain stationary andlikewise the planetary cage or gear |56 will also remain stationary.Under these conditions then, with the gear |28 rotating at propellerspeed and 4since it engas 7the gear Mya driving train will 'bef-providedthrough the-sun gear |44, the planetary pinions |50 and |52, through thegears |48 uand |46 and finally to the gears |22 and |20.

This driving .connection just described in effect vtlien,-providesiafsimple step-up, step-down gear ltrain which results indriving the gears |20 and bevel 4gears |64 will rotate the control gear|60 and the planetary cage A|56 so that the planetary pinions A|50 and4152 -will revolve about their .respective sun gears |44 and |48 so asto vary the resultingvdriven speed vof the .gear |46 and the gears |22and |20. This variation in speed of the gears |l20 and |22 thenrepresents an increaseor'decrease, as the case may be, from therotational speed of-.the propeller so that relative movement ineither-direction is .obtained vbetween the lgear :L20 Vfand thedistributor valve drive gear |30. As a'result, the distributor :valve`drive '-nut will .cause asubsequent reciprocating movement in thedistributor lvalve :so as to vary the pitch of the propeller blades.

.A second .planetary gear cluster |80 has :also -provided asanfoperative connection r`between the propeller and the .servo vcontrolinput `,shaft .|02 whosepurpose will be described hereinafter. The gearcluster |80 comprises a normally drivengear |04 which rengages the 'gear|28 gand, therefore, yis driven Ein timed relation to, and 'by the`rotation of, azpropeller. A sun gear |86 is .driven by 'the gear |8'4and engages :a planetary pinion |88 whichin turn'meshes with theinternal teeth of athe ring gear |90. :Since the ring gear meshes withthe `normally'ifixed gear ||2 through .a re- 'versing gear |92,":it alsowill `be held stationary during-normal operation. "As a result, the:planetary pinion |88 will'revolve about .the'sun gear .|86 and .therebythrough rits shaft '|.961the bevel gears |98 and the servo control inputshaft .|82 will be rotated.

previously wzlesczribed, lthe normally station- Iary gears ||0 and?|.|.'2 yprovide for yoperation of 'the hub'carried .pumps when -thepropeller -is rotating. Itis 'themapparent that some means is 'necessaryto operate these pumps so that-high pressure fluid for propeller -pitchchange is availablewhen the propeller is not rotating, as -for example,when it is desired to unfeather the -provpeller 'in ight -or on -theground. To this end V'tation of the'normally rstationary gears 4H0 andVI|2 'in-one direction only, i. e., to prevent inadvertent motion-of thenormally stationary gears ||0 and ||2 Aduring normal operation when thelreaction -of the pumps is imposed thereon.

Itisfthen-apparent'that during operation ofthe auxiliary motor the gears||0 and '|12 will'be rotatedso as 'to provide drivingpower `for=thepropeller Vpumps While "at lthe lsame time providing driving powerthrough vthe `reversing 4gear 92 to the planetary cluster |80 and theservo control input shaft |82. Hence, under these conditions with thepropeller stopped the sun gear |86 of the gear cluster |88 will be heldstationary due to the fact that its driving gear |84 and gear |28 arealso stationary. With the ring gear |56 now rotating, the planetarypinion |88 will revolve about the sun gear 86 so as to rotate the bevelgears |68 and the input shaft |82. With the in put shaft now rotating inthe same direction as it does when the propeller is rotating, the servosystem to be described in connection with Fig. 2 then operates toproduce the desirable controln ling movements in the output shaft |68 toeventually move the distributor v-alve as desired.

The particular gear train connections described herein are claimed inco-pending patent application Serial No. 159,772, filed May 3, 195|),byNelson R. Richmond.

Referring to Fig. 2, the servo control input shaft |62 is shown asdriving the gears 220 of a servo pump which provides high pressure oilto the servo controller system. The supply of fluid for this pump isomitted for convenience. The high pressure oil from the servo pump issupplied to a manifold 222 which in turn distributes the oil to a springloaded relief valve 224, to a low pressure switch 226, to the high pitchside or chamber 228 of the servo rack and to the proportional solenoidvalve 230 which acts as a metering device for the servo system. Afterthe meo tered oil leaves the pilot valve 230 of the proportionalsolenoid, itis routed via a line 232 to a norm'ally closed chamber 234of a reversing solenoid 236. The metered oil from the pilot valve 236 atthe same time is routed through the passage 240 through a toppinggovernor which is driven by the input shaft |82 and includes a valve 242operated by the spring loaded fly weights 243. The metered oil normallypasses through a topping governor valve 242 and ows via the line 244 toa chamber 246 of the reversing solenoid valve and to the low pitch sideor chamber 248 of the servo rack.

A servo rack comprises a stationary piston 250 and a moveable cylinder252 which carries the rack teeth 254. When the servo rack is actuatedink either direction it actuates the servo output shaft |68 through thegears 256.

Inasmuch las the output shaft |68 eventually transmits motion to thedistributor valve in the propeller hub, a lock pitch unit is coupled tothe output shaft to provide selective locking thereof against rotation.The pitch lock unit responds to selective electrical signals from thepropeller control relay box or the lock pitch switch 226, the lock pitchswitch providing automatic operation upon a failure of servo hydraulicpressure by means of electrical line 260.

The pitch lock unit comprises a pair of toothed disks 262 and 264 whichare fixed to the output shaft |68. The teeth on the disk 262 are slopedin an opposite direction from those on disk 264 so that a lockingengagement with either of the disks by the locking members 266 and 268will prevent rotation of the output shaft |68 in one of two directions.In other words, the locking member 266 will prevent rotation of theoutput shaft |68 toward a high pitch direction but will ratchet away soas to permit free movement in 'a low pitch direction. The locking member268 on the other hand by engagement with the disk 262 prevents rotationof the output shaft |68 in a low pitch direction only. Of course,simultaneous engagement of both the locking members 266 and 268 with thedisks 264 and 262 would lock the out- Dutshaft |68 against movement ineither direction.'- lThe locking elements 266 and 268 are biased in anengaging position by means of a pair of coil springs 210 and are heldina disengaged position by the solenoid coils 212 and 214. The solenoidcoils are in turn energized by signals received from the propellercontrol relay box which comprises the various electrical controlelements and switches for operation and propeller control.

The servo-unit lock system and associated mechanism is claimed inco-pending patent applicationSerial No. 159,736, filed May 3, 1950, byMelvin E. Longfellow, now U. S. Patent Serial No. 2,652,122, issuedSeptember 15, 1953.

In operation then (referring to the servo control systeml the output ofthe oil pressure pump 220 of the servo pump is maintained at a desirablepressure by means of the relief valve 224. This pressure always reactson the servo rack tending to move it in a high pitch direction. Thismovement toward high pitch is resisted by the metered oil from theproportional solenoid pilot valve 230 which valve is adjusted inresponse to the signals received from the electronic governor. Theelectronic governor causes the pilot valve 230 to increase the meteredoil flow to the servo rack and move the output shaft in the low pitchdirection when the propeller R. P. M. is below the desired setting. Asthe propeller R. P. M. is higher than the governor setting, the pilotvalve 230 shuts off the metered oil flow and opens the metered oilpassage to drain which permits the servo rack and the connecting gear256 to the output shaft |68 to move in the high pitch direction. The lowpitch to high pitch area ratio of the stationary piston 250 of the servorack may be in the order of two to one so that in the on speed conditionthe metered oil pressure is approximately one-half the magnitude of theservo pump output pressure.

The fly ball type topping governor may be set for some desired R. P. M.as for example for of maximum desirable propeller R. P. M. to provide asafety measure against sudden excessive propeller rotational speeds asmight, for example, result in a high speed turbo-driven propellerarrangement. Thus, in the event that the normal governing system fails,the topping governor regulates the now of oil to the servo rack by meansof its valve 242 to maintain constant propeller y R. P. M. at thetopping governor overspeed setting. Since the topping governor controlsthe propeller at a relatively low rate of pitch change, Ia ball checkvalve 280 is provided in the reversing solenoid valve to permitby-passing of the topping governor in the event of a requirement for ahigh rate of increase pitch change is required such as would occur whenfeathering from an overspeed condition.

For reverse pitch operation both the reversing solenoid and theproportional solenoid are energized to permit direct high pressure servooil iiow to the low pitch side of the servo rack and to isolate thetopping governor from the system to prevent it from calling for a pitchchange in the wrong sense if an overspeed occurs in reverse. Theby-passing is accomplished by unseating the ball check 280 in thereverse solenoid 236. With the ball check unseated, high pressure oil,which in metered form is leaving the pilot valve 230 into the line 240,will be permitted to flow via the line 232 through the normally closedchamber 234 of the reversing solenoid valve 236 past the open ball check280 and into the chamber 246 ofthe valve from whence it may owdirectly'to the low pitch chamber 248 of the servo rack. Y

For feathering, the proportional solenoid is energized in the high pitchdirection to allow a direct high pressure oil flow tothe high pitch sideor chamber 228 to move it to the extreme high-pitch position. In otherwords, by energizing the proportional solenoid in-an extremehigh pitchdirection causes it to no longer meteroil into the line 240 so that nopressure whatsoever is admitted to the low pitch side of the servo rack.A

Since the position of the servo controller output shaft is a directindication of propeller blade angle, a pitch stop cam mechanism 290 isconnected directly to the shaft |68 by means of gears 292. The cammechanism consists of five adjustable cams to provide a normal highpitch limit, a normal low pitch limit, a reverse limit, a feather limitand a starting limit which would correspond to an approximate zero pitchblade angle. Each of the individual cam elements are arranged toselectively trip electrical limit switches 294 which in turn disable thedesired portion of the electrical system con-tained in the propellercontrol relay box.. v

In order to sensitize'the operation of the electronic governor and itsoutput signal to the propeller solenoid, a feedback potentiometer hasits movable element connected to the shaft- 256 which carries the p-itchstop cam mechanism 220. Hence, the movements of the servo output shaft|68 will provide a simultaneous variationv of potential output of thepotentiometer which output is fed back as a signal to the electronicgovernor to provide in effect an anticipator or follow-up signal.

Fig. 3 illustrates the various electrical units which represent thepropeller control lrelay box and diagrammatically indicates the variouselectrical communications therein. Each Vof the previously mentionedelectrically operated elements are also shown diagrammatically herein,as for example the auxiliary motor and lock pitch solenoids. Forconvenience, the specific electrical wire connections are not enumeratedthroughout. For convenience of description instead, the generaloperation of `each of these switches and the result produced on theoperating electrical elements is generally described. As previouslymentioned, one limit switch isV provided for each propeller stopposition and these in addition to the other electrically responsiveelements are diagrammatically indicated along vthe right hand side ofFig. 3. v

During normal governing operation the increase and decrease pitchsolenoids are held energized through the normal lowv and normal highpitch limit switches. Then,lif for anyieason the governor servo systemFig.`2) moves toa lower pitch than ythe setting of the normal low pitchlimit switch, the Yassociated Acam will trip this switch to open thecircuit to the low pitch solenoid ofthe pitch lock and preventthe outputshaft |68 of the servo unit from moving any furthertoward lowpitch.Following this, Yshould the governor servo system move again toward highpitch the output shaft |68 willratchet away from its locked positionuntil the low pitch limit switch is returned to normal (as forexample'by spring loading). The low pitch solenoid 212 of .the pitchloch unit will again be energized to`- disengage the lock. The normalhigh pitch limit switch will loci; the servo output shaft in-a similarmanner by del-energizing the highpitch solenoidv 214'of the pitchv lockunit.

In the event vthat the feather switch is operated, a plurality ofcircuits are completed or closed. First, the holding coil 300 of thefeathering switch is energized under the control of the closed featherlimit switch. Second, the increase pitch relay is energized so that itopens the governor circuit and simultaneously applies battery current tothe governor proportional solenoid with a polarity to causethe governorservo system to operate in a high pitch direction. Third, the high pitchsolenoid 211| of the pitch lock unit is held energized (unlockedposition) independently of the normal low pitch limit switch. Fourth,the relay 3|() is energized so that the switch 3|2 is closed to providecurrent to the auxiliary motor. Following this, the servo output shaft|68 actuates the distributor valve within the propeller hub to move theblades toward a feather position, keeping in mind that the position ofthe servo output shaft |68 is a direct indication of blade pitchposition when the servo output shaft has moved to the feather position.The feathering cam will actuate the feather limit switch toward an openposition to open the holding coil 352i of the feathering lswitch whichwill cause the switch to return to normal position. At the same time thehigh pitch solenoid 2"."4 of the pitch lock unit is de-energized so thatits corresponding spring 219 (Fig. 2) will engage the lock preventingfurther movement of the servo output shaft toward a higher pitch, i. e.,beyond feathering. As a precautionary safety measure, it is possible tooverride the cie-energizing operation of the feather limit switch byfurther manual operation of the feathering switch in a featheringdirection.

To unfeather the propeller, the unfeathering switch is moved toward theUF position which energiaes the unfeather relay via the line 320; andsince in moving tc the feathered position the normal high pitch limitswitch had been moved to the dotted line position, the relay 3|!! (forthe auxiliary motor) is energized also as follows. Battery current flowsfrom the lock pitch switch via the line 324, through the high pitchlimit switch (in dotted position), through line 326 and the line 328adjacent the unfeather relay switch (which is now closed) and finally toline 330 and the relay 3| (l to energize the auxiliary motor. rihus itwill be apparent that when the servo shaft returns to the -high pitchlimit switch setting this switch will return to its normal (full line)position to de-energize the auxiliary mo- At the same time that currentis owing from the lock pitch switch (Via line 324) as described above(for energizing the auxiliary motor), current will also flow through thenormal low pitch limit switch via line 334 back through connection 336and then via line 338 to energize the low pitch lock solenoid 212 towardan unlock position thus ernitting movement toward low pitch (unfea- Atthe same time since the propeller is not rotating, or is beginning toslowly rotate, the electronic governor will call for a reduced pitchthereby signalling the proportional solenoid accordingly.

It shouldbe noted that both a governor solel10id" and a proportionalsolenoid are illustrated 1n F1a 3 as being connected in parallel.Although both solenoids are required .to provide governing powerhavinghigh rate of response, the dual installation provides a safety featurein the event one solenoid becomes inoperative.

In order to obtain reverse pitch the reversing switches are closed.rI'wo reversing switches are shown with the switch adjacent the batteryterminal serving as a safety switch operable to a closed position byengagement of .the aircraft landing gear with the ground in a mannerwellknown in the art. With the switches closed, current then fiows fromthe battery to lines 35B, 352, 354 to energize the reversing relay. K Atthe same time the decrease pitch relay is also energized through lines356, 358 while thereversing solenoid is energiz-ed via line 3dB.

It is apparent that the decrease pitch relay will open the circuit fromthe electronic governor and will apply battery current with properpolarity to the proportional solenoid via the contacts of the decreasepitch relay so as tok decrease pitch toward a reverse position.

The reversing relay energizes the low pitch lock solenoid (to permitmovement toward low pitch) via the line Sill, the reverselimit switch,line 312, junction 335 and line 338. It Willbe noted thatthis circuitwill beopened when the reverse limit switch is operated to an openposition by its cam. The reversing relay when energized alsosimultaneously conditions the unreversing relay by energizing the lattervia line 380. This connects the unreversing relay with the normal lowlimit switch which is held inthe dotted line position by its camwhentheservo output shaft moves to reversing position. Thus theunreversing relay will be held in this position by obtaining currentfrom the lock pitch switch, the low pitch limit switch, line 382 andjunction 384 even when the reversing relay is subsequently de-energized.

When the reverse limit switch is opened (when the propeller blades reachproper reverse position) the low pitch lock solenoid 212 is de-energizedto lock the servo input shaft against movement toward low pitch.

In order to unreverse the reversing switch is returned to normal, asshown, and the reversing relay is de-energized. Although suchde-energization breaks the flow of current to the line 380 of theunreversing relay, the latter is still energized by the contacts of thenormal low limit switch (dotted line position) so that consequently theincrease pitch relay is energized.

The increase pitch relay thereafter opens the circuit from theelectronic governor and simultaneously directly energizes the governorand proportional solenoid to actuate the governor servo system towardhigh pitch. As the servo system moves past the normal low pitchposition, the low limit switch is returned to normal therebycie-energizing the unreversing relay which in turn de-energizes theincrease pitch relay to return the pitch control to the electronicgovernor.

When starting a turbine power plant (turboprop installation) it isdesirable to have the propeller blades in fiat pitch. Thus when thestarting switch is operated the decrease pitch lrelay operates todecrease pitch, the starting relay ope-rates through the normal contactsof the starting switch, the relay 3! operates the auxiliary motor (toobtain pump pressure since the propeller is not rotating) and the lowpitch lock is energized to an unlock position. The propeller servosystem then moves toward low pitch until the start limit switch isopened by its respective cam. This de-energizes the starting relay andthe auxiliary motor relay 3 I0 while the low pitch .lock isde-energ'ized into a ,lock position and the 10 blades are then in flatpitch. When the turbin power plant starts, the starting switch isreturned to normal thereby yde-energizing the decrease pitch relay andreturning control to the electronic governor.

A manual lock pitch switch is provided for manually de-energizing thehigh and low pitch lock solenoids 212 and 214 to lock the servo systernoutput shaft I 68 against movement in either direction. v

It is therefore apparent as a result of this invention that an improvedpropeller system has been provided having an overspeed system whichwillprevent sudden excessive'R. P. M. surges while being disabled whenreversed pitch is being called for. Thus in any event the overspeedgovernorwill not be calling for an increase in pitch (toward positivefrom negative) when a. negative or reverse pitch is desired.

Although onlv one embodiment of this invention has been illustrated anddescribed herein; it

is apparent that various changesandmodifications may be made in theconstruction and arrangement of the various parts without departing fromthe scope of this novel concept.'

What it is desired to obtain by'Lett'ers Patent l. In an aircraftpropeller comprising variable pitch blades, power operated meansforvarying the pitch of said blades in positive and negative pitchpositions including a source of power therefor, controlling meansoperatively connected to said pitch varying means and said source' of.power for controlling said pitch varyingr means; speed responsive meansfor governing said controlling means including a servo motor operativelyconnected to. said controlling means, overspeed'gov'- erning meansoperable to preventpropeller speeds beyond a predetermined maximumduringp'ositive pitch positions of said blades. said overspeedgoverning-means including operative connections to said servofmotor, andmechanism for signalling said controlling means for a negative pitchposition of said blades including-means for disabling said overspeedgoverning means, said mechanisrn comprising operative connections ktosaid speed responsive means and said servomotor. i

n 2. In an aircraft propeller comprising variable pitch blades, poweroperated means for varying the pitch of said'blades in positive andnegative pitch positions including a source of power therefor.controlling means operatively connected to said pitch varying means andsaid source of power for controlling said pitch varying means, speedresponsive means for governing said controlling means including aservomotor operatively connected to said controlling means. overspeedresponsive governing means operable toy prevent propeller speeds beyonda predetermind maximum during positive pitch positions of said blades,said overspeed governing means including operative connections to saidcontrolling means and said servomotor and manually controlled mechanismfor signalling said control means for a negative pitch position of saidblades including means forming a part of the operative connections ofsaid overspeed governing means for isolating said overspeed governingmeans from said control means said manually controlled mechanismcomprising operative connections to said speed responsive means and saidservomotor. 3. In a propeller comprising variable pitch blades. meansfor varying the pitch of said blades in positive and negative pitchpositions, means for controlling said pitch varying means including asource of power therefor, speed responsive means for governing saidcontrolling means including a rst valve actuated thereby, said valvebeing operatively connected to said controlling means for actuating thelatter, overspeed responsive governing means for maintaining the speedof said propeller below a predetermined maximum including a second valvein series with said rst valve and forming an operative connection fromsaid first valve to said controlling means, and manually controlledblade reversing mechanism having operative connections to said valvesfor positioning said control means in a negative blade pitch positioncomprising means for disabling said overspeed responsive governing meansand includingY an operative connection to said controlling means.

4. In a propeller comprising variable pitch blades, means for varyingthepitch of said blades in positive and negative pitch positions, meansfor controlling said pitch varying means including a source of power anda servomotor, said controlling means being operatively connected to saidpitch varying means, a speed responsive governor for governing saidcontrolling means f including a rst valve actuated thereby, said valvebeing operatively connected to said servomotor, an overspeed responsivegovernor for maintaining the speed of said propeller below apredetermined maximum when said blades are in positive pitch positionsincluding a second valve in series with said first valve and forming abridging connection between said first valve and said servomotor, andpitch reversing means operatively connected to said servomotor and saidvalves including mechanism for lay-passing said overspeed responsivegoverning means, said reversing means comprising operative connectionsto said valves and said controlling means.

5. In a propeller according to claim 4 including pitch stop means fordisabling said reversing means and said by-passing means when saidblades reach a predetermined negative pitch position.

6. In a propeller comprising variable pitch blades, means for varyingthe pitch of said blades in positive and negative pitch positions, asource of power, means for controlling said pitch varying meansincluding operative connections to said source and said pitch varyingmeans, speed responsive means for governing said controlling meansincluding a servo system therebetween,

said system comprising a servo source of power, 'a servomotoroperatively connected to said controlling means, and a valve movable inresponse to said yspeed responsive means for controlling said motor andoperatively connected to said servo source of power, an overspeedresponsive governor including a valve movable thereby, said lastmentioned valve having connections to said servomotor for limitingpropeller rotational speed above a predetermined value, and manuallyoperated means for signalling said first mentioned valve for a decreasepitch position including mechanism for disabling said overspeed governormeans including operative connections to rst valve and overspeedgovernor means.

7. In a propeller comprising variable pitch blades, means for varyingthe pitch of said blades in positive and negative pitch positions, meansfor controlling said pitch varying means, speed responsive means forgoverning said controlling means comprising a first valve actuatedthereby, a servomotor operatively connected to said rst valve and saidcontrolling means for energizing said controlling means, a servo sourceof power controlled by said first valve, an overspeed responsivegovernor including a second valve operable thereby, said second valveincluding operative connections to said rst valve and said servomotorfor limiting the maximum speed of rotation of the propeller.

8. In a propeller according to claim 7 including a third valveoperatively connected to said second valve and said servomotor, andmeans for signalling said control means for a reverse pitch positionincluding conduits connected to said third valve and providing fordisabling said second valve.

MELVIN E. LONGFELLOW. NELSON R. RICHMOND.

References Cited in Vthe file of this patent UNITED STATES PATENTS

